Bisphenol-A (BPA) is either a harmless chemical that’s great for making plastic or one of modern society’s more dangerous problems. Depends whom you ask.

BPA is in many types of plastics and the epoxy resins that line most aluminum cans, as well as thermal papers like receipts. It is an endocrine disruptor that mimics estrogen, a hormone especially important in sexual development, and the fact that it’s all over the place worries many people. Newsweek spoke with about 20 scientists, leaders in the field of BPA research, and the majority say it is likely (though not certain) that the chemical plays a role in a litany of health concerns: obesity, diabetes, problems with fertility and reproductive organs, susceptibility to various cancers and cognitive/behavioral deficits like ADHD.

“There's too much data consistent across studies…time and time again…to ignore it and suggest BPA has no effect on humans,” says Gail Prins, a physiologist at the University of Illinois at Chicago.

But the plastic industry, researchers it funds and, most important, many regulatory agencies—including the U.S. Food and Drug Administration (FDA and the European Food Safety Authority (EFSA)—say BPA is safe for humans at the levels people are exposed to.

“BPA used in food packaging does not present a risk to consumer health,” says FDA spokeswoman Theresa Eisenman. Kathryn St. John, with the industry group American Chemistry Council, says BPA is safe and refers to statements made by the FDA and EFSA to back her up. And John Rost, chairman of the North American Metal Packaging Alliance, states emphatically that BPA is nothing to worry about, adding, “I feed it to my five children every day.”

Fetal Risks

BPA was first synthesized in 1891 by a Russian chemist and investigated for use as an artificial estrogen in the 1930s, when it was found to mimic the effects of that hormone on the human body. Two decades later, manufacturers began to use it to make plastics, specifically polycarbonate, and its estrogenic properties were mostly ignored.

BPA is relatively cheap to produce and very effective for making structurally sound plastics, producing strong and often transparent products that resist falling apart when heated or cooled. And it’s great at keeping cans from corroding. Around 75 percent of cans in North America are lined with BPA, says Rost. And, thanks largely to BPA resins, there hasn’t been a single case of fatal food-borne illness traced directly to North American cans in 37 years, because the substance prevents metal corrosion and breakages, he says.

The use of BPA has continued to grow in the past few decades. As of 2012, 10 billion pounds of the material were produced worldwide, with a total estimated 2013 market value of more than $13 billion. And the market is expected to expand by about 5 percent annually in the near future. Every day, the manufacture and sale of BPA brings in tens of millions of dollars.

But scientists suggest that might be offset by a large, hidden cost: its impact on human health. To date, there have been around 1,000 animal studies on BPA, and the vast majority show that it causes or is linked to many health problems, from alterations in fertility to increased risk for cancers and cardiovascular problems to impaired brain development, says Frederick vom Saal, a longtime researcher of the product at the University of Missouri-Columbia.

There have only been animal studies because it would be unethical to give extremely high doses to humans, says Ana Soto, an endocrinologist at Tufts University. While testing on animals can be a good starting place to understanding how a chemical might affect human bodies, such tests aren’t conclusive. For that reason, scientists have conducted about 100 human epidemiological studies to look at the patterns of health and disease in real-life settings. These too show a correlation between exposure to BPA and the aforementioned ailments.

Scientists are particularly worried about exposure to the developing fetus and infants. When the fetal brain is first developing, it is most vulnerable to endocrine disruptors like BPA, research has shown. And animal studies have suggested early exposure to BPA has a significant impact on the brain and other organs. Some epidemiological research does too. Brown University epidemiologist Joseph Braun, for example, has shown a link between early childhood exposure to BPA and later behavioral problems.

The majority of the animal studies to date have involved large doses, quantities much greater than, we think, most humans encounter. But we don’t really know.

It’s in Your Blood

Several dozen studies in the past five years or so have found average human blood serum levels of BPA in the low range, around 1 part per billion (ppb). Many of the negative health effects in animal studies have been shown to occur at these levels, says Laura Vandenberg, who researches endocrine disruptors at the University of Massachusetts, Amherst. But the established methods for testing the toxicity of substances—the degree to which they can harm the human body—assume that the toxic impact is more or less proportional to the amount ingested. Endocrine disruptors like BPA, which act like hormones, don’t “play by the rules,” says Patricia Hunt, a geneticist at Washington State University. Hormones can have very different effects at low and high levels. An estrogenic chemical can induce cell growth at low levels but inhibit it at high concentrations, for example. Regulatory agencies have begun to recognize this but still “keep relying on standard toxicology tests,” Hunt says.

The FDA contends the studies that show exposure in the low ppb range must be outliers, the result of what the FDA’s Eisenman calls the “well-known problem of contamination” that occurs during the collection of blood samples. BPA is also found in dust, and scientists all agree that it’s very hard to avoid contamination when testing for this chemical. But it’s not impossible. Many researchers say a handful of labs have established protocols to control for contamination. One 2014 round-robin study (where blood with known concentrations of BPA was tested at different institutions) found that three labs accurately identified and measured samples with very low levels of BPA, while one lab failed, Vandenberg says. The paper also established contamination-avoiding guidelines labs can and now do follow, she adds.

Research on the impact of BPA on human health is contradictory. Baldomero Fernandez/Gallery Stock

And as reported in late 2014 by vom Saal and a colleague in Molecular and Cellular Endocrinology, nine studies that employed contamination-avoiding methods (such as testing background levels of the chemical) found human BPA serum levels close to or above 1 ppb.

Justin Teeguarden, a researcher at the Pacific Northwest National Laboratory, published a study last month investigating the impact of consuming soup containing six times the FDA’s acceptable daily intake (which is five micrograms per kilogram of body weight, according to Eisenman). The 10 men tested ended up with blood concentrations of BPA of about 0.1 ppb, 10 times lower than levels found in vom Saal’s review. Teeguarden says the vast majority of people probably have BPA blood levels much lower than this, since these subjects were exposed to thousands of times “more BPA than most are exposed to.”

But Teeguarden’s characterization of standard exposure might be missing a key element: non-food sources. BPA can get into the bloodstream from handling receipts, for example. And when the chemical gets into the body this way, says vom Saal, it bypasses the liver, which normally renders harmless a good amount of ingested BPA. This leads to significant levels of the chemical in the blood stream, a 2014 JAMA, The Journal of the American Medical Association study showed. Vom Saal argues that the FDA, EFSA and other regulatory agencies have not yet addressed—or even recognized—how much these sources of BPA exposure are contributing to human blood concentrations.

Teeguarden disagrees, though, taking the same basic position as the FDA: The blood levels reported by vom Saal and the others are all wrong, due to contamination. But it is worth mentioning that Teeguarden’s study was funded by the American Chemistry Council—a trade group that represents companies that manufacture chemicals like BPA. The council has funded other studies on BPA, and they’ve all concluded that the chemical has no harmful effects. One 2006 analysis by vom Saal and Wade Welshons showed that 11 out of 11 industry-funded studies found BPA had no significant action, while 109 of 119 studies that had no industry funding (92 percent) did find effects of BPA.

“It’s puzzling when you see that kind of disparity—it doesn’t make sense from a scientific perspective,” says Andrea Gore, a professor of pharmacology and toxicology at the University of Texas at Austin and editor-in-chief of the journal Endocrinology. Dr. Csaba Leranth, a Yale School of Medicine physician and scientist whose studies have shown that BPA reduces the number of synapses (brain cell connections) in monkey brains, is more direct: “Studies funded by industry are not reliable.”

In June 2014, the FDA reiterated that BPA is safe in the way it is currently used by plastics manufacturers. But the agency also dismissed as irrelevant the vast majority of the BPA safety studies its own scientists reviewed in preparation for that official position statement. According to the FDA, for example, all of the 48 epidemiological studies reviewed had “no utility” for the agency’s risk assessment, the formal process it undertakes to decide if a chemical is safe for human health or not.

In some cases, the reviewers’ notes don’t seem to match up with the FDA’s sweeping assertion that there’s nothing to see here. For example, the reviewers wrote of one 2013 study, “These data support a plausible relationship between urinary BPA levels and obesity.” They say that another paper, regarding hyperactivity, “should be considered as part of the growing body of work assessing relationships between BPA exposure and behavior.” But none of these seemingly concerning links are mentioned in the conclusion that BPA is safe.

“I think there’s a strong influence among the chemical industries and their lobbyists—they have the money and time,” Gore says, adding that researchers have very little of both. In 2013, for example, the American Chemistry Council spent more than $11 million on lobbying expenses, according to the Center for Responsive Politics. Industry groups have also funded, and in some cases written up, research done by governmental scientists. One 2008 investigation, by the Milwaukee Journal Sentinel, found that “a government report claiming that bisphenol-A is safe was written largely by the plastics industry and others with a financial stake in the controversial chemical.”

The Chemical Whack-a-Mole Game

Despite the FDA’s continued support of BPA, the chemical is already being replaced on the market due to consumer concerns—but with substances such as bisphenol-S that behave similarly, and may even be worse in some ways. This often happens when companies find that a substance they use may be harmful or is shunned by consumers, and they need to find a publicly acceptable replacement, something Braun calls the “chemical whack-a-mole game.”

There are numerous examples where industry has tried to sow doubt to keep products on the market when there is evidence to reasonably conclude they might not be safe, says Dr. Philippe Grandjean, a health researcher and physician at Harvard. Lobbying by chemical companies allowed lead to be used in gasoline for decades longer than necessary, and this needlessly damaged the developing brains of thousands of children, he says.

The case is not as clear-cut with BPA, because of inconsistencies and uncertainty in the data, says Heather Patisaul, an endocrinologist and developmental biologist at North Carolina State University. “We don’t really understand how these things affect us at low levels, and what that means over a lifetime,” she adds.

But most scientists polled think there’s enough “writing on the wall,” as vom Saal puts it, to enact more stringent regulations, at least while BPA is being studied more thoroughly. “You have to act or not,” says Soto, despite the uncertainties. “I think we have plenty of evidence, if we are responsible, to act.”